The long term goal of this project is to understand how adhesive interactions induce and integrate intercellular signaling between monocytes and neutrophils, which are leukocytes of the myeloid lineage, and endothelial cells. We also will determine how these interactions influence subsequent functional responses of the leukocytes in homeostatic inflammation and in inflammatory disease. The change in title of the project from "Molecular Mechanisms of Neutrophil Adhesion to Endothelium" to "Molecular Interactions of Myeloid Cells with Endothelium" reflects a larger scope, including a focus on adhesion-dependent signaling mechanisms and new investigations of the interactions of monocytes with endothelium, in addition to studies of PMNs. Specific adhesion molecules tether endothelial cells and myeloid cells together; similarly, such tethering molecules can bind platelets to myeloid cells and can mediate adhesion between the myeloid leukocytes themselves. We will determine how these adhesive interactions lead to the generation of intracellular signals that alter critical inflammatory functions of the myeloid cells. We will focus on expression of immediate-early genes, on cell spreading, and on related cellular responses. We will determine how molecules known to tether myeloid leukocytes transmit signals, and orchestrate them when acting in concert with other factors. Using isolated myeloid leukocytes and cultured endothelium, transfected cells, model membranes and purified molecules, we will characterize the roles of selectins, in Specific Aims l and 2. In Specific Aim 3, we will use similar strategies to identify tethering and signaling mechanisms of ICAM-3, a new member of the ICAM family, in myeloid cell interactions. In Specific Aim 4, we will examine "outside-in" signaling by beta32 (CD11/CD18) integrins in myeloid cells using two traditional approaches, adhesion of leukocytes to specific ligands and incubation with antibodies that may induce functional alterations, and a novel approach - study of myeloid cells with targeted deletions of individual CD11/CD18 heterodimers. Information from these reduced systems will then be used to analyze complex models of inflammation (cell-cell interactions in vitro) and, ultimately, to identify new strategies for understanding and modifying inflammatory events in vivo and in humans.